Pneumatic radial tires reinforced with steel cords have a disadvantage in that when they are used in a corrosive atmosphere rust occurs in the steel cords which lowers the tensile strength of the steel cords and deteriorates the adhesion between the steel cords and the rubber composition.
Rust in steel cords is caused by rain water or the like penetrating external injuries in the belt layers or a ply layer of the pneumatic radial tire. In addition, when a tire is set with a tube, a flap and a rim, water or the like remains in the gap between the tire and the tube. Over the course of time, the water or the like permeates the steel cords through the inner liner portion of the tire and causes rust in the steel cords.
Various attempts have been made to overcome the above-identified rust problem. Examples of the attempts include:
(1) employing from 0.1 to 3.0 parts by weight of an aromatic triazole in the rubber composition surrounding the steel cords, (see U.S. Pat. No. 4,169,112); PA0 (2) employing metal salts of para-oxybenzoic acid and cobalt salts of fatty acids in the rubber composition surrounding the steel cords to improve the adhesion between the steel cords and the rubber composition (see Japanese Patent Laid Open No. 1356/77); and PA0 (3) employing a protective layer surface comprising a rust preventing material consisting of a surfactant and a film-former on the surface of the steel cords (see U.S. Pat. No. 4,330,592). PA0 (1) a cylindrical tread portion; PA0 (2) side portions located at both sides of the tread portion and extending inwardly in the radial direction; PA0 (3) bead portions located at the inner edge portions of the side portions; PA0 (4) a carcass comprising at least one ply which is reinforced with a belt arranged on the inside of the tread portion, wherein said belt and/or said ply is reinforced by steel cords; and PA0 (5) a rubber composition surrounding the steel cords, wherein said rubber composition comprises: PA0 (1) a cylindrical tread portion; PA0 (2) side portions located at both sides of the tread portion and extending inwardly in the radial direction; PA0 (3) bead portions located at the inner edge portions of the side portions; PA0 (4) a carcass comprising at least one ply which is reinforced with a belt arranged on the inside of the tread portion, wherein said belt and/or said ply is reinforced by steel cords; and PA0 (5) a rubber composition surrounding the steel cords, wherein said rubber composition comprises:
However, when tires are exposed to severe running conditions for a long period of time, the above-described attempts have not proved satisfactory.